Guarantee the confidence classes give of providing it? (9)

I believe the answer is:

assurance

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'guarantee' is the definition.
(I've seen this in another clue)

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(Other definitions for assurance that I've seen before include "Confidence, composure" , "Confidence, certainty" , "Word given" , "Confidence; security" , "Cure an ass of a feeling of certainty" .)

I've seen this clue in the Evening Standard.

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